Sterilization indicator coating



United States Patent M 3,288,718 STERILIZATION INDICATOR COATINGConstantine Carumpalos, Mountainside, N.J., assignor to United StatesEnvelope Company, Springfield, Mass, a corporation of Maine No Drawing.Filed Nov. 26, 1963, Ser. No. 326,190 6 Claims. (Cl. 252408) Thisinvention relates in general to the preparation of matter for visuallyindicating whether or not that matter has been subjected tosterilization conditions. More particularly, the invention relates tothe preparation of articles, usually of paper or similar material, bythe application thereto of a particular kind of coating preferably inthe form of an ink, which changes from one distinct color to anotherwhen the article on which it is applied is subjected to sterilizationconditions, to indicate that sterilization conditions have beenattained.

This invention is especially applicable in the sterilization of medicalinstruments, formulacontaining baby bottles, or the like, at hospitals.For instance, the need for adequate control measures in infant feedingto reduce the death rate of new-horns is recognized as a basic challengeto hospitals throughout the world. Among the known preventable causes ofdeath in infants, infections are recognized as being one of the mostimportant. It has become the practice in a good many hospitals to applydisposable protective caps to formula-containing bottles before they aresterilized. The 'bottles and caps are thus sterilized together, and thecaps remain on the bottles until they are ready for use to preventcontamination subsequent to sterilization.

In such sterilization procedures, it is necessary that the bottles whichhave been completely sterilized be capable of ready identification. Itis necessary to be able to visually identify bottles which have beensterilized, as distinguished from unsterilized bottles in the event ofaccidental inte-rmingling of bottles, some, but not all of which havebeen sterilized.

It is an object of this invention to provide the articles with a coatingwhich will change from one distinct color to another only whensterilization conditions have been attained.

It is a further object of this invention to provide a coating forarticles which are to be sterilized, which may be printed as an ink ontosuch articles, and which is resistant to premature color changes instorage under adverse-temperature and humidity conditions.

Other objects will appear hereinafter. The ultimate objective of theinvention, of course, is to reduce the number of infections in hospitalsby using only articles which are absolutely sterile.

In the manufacture of paper caps for baby-formula containing bottles,for example, there are certain requirements which must be met by theindicator coating before it will be acceptable. In the manufacture ofsuch caps, it v is desirable to print words, strips, or other markingsin such a manner that a change in color thereof will be readily visible.The paper caps are very often stored for long periods of time, possiblysix months or even longer, before use. In certain parts of the countrywhere Warm and humid weather conditions exist, the indicator coating onthe paper caps must resist premature color changes. If a premature colorchange occurs, then the entire stock may become useless, or even Worse,if the premature color change goes unnoticed, a false indication ofsterilization may exist on non-sterile articles. This, needless to say,may bring about serious results.

Furthermore, the color-changing sterilization indicator should be aliquid capable of being applied to the articles which are to besterilized by ordinary printing machinery. Paper caps for baby formulabottles are manufactured by 3,288,718 Patented Nov. 29, 1966 themillions, and the only feasible way of applying the indicator coating isby a printing process. The coating must not be adversely affected, as bynoticeable fading or running, by the moisture in steam sterilization.

The coating composition used in the present invention basicallypossesses the physical characteristics of an ink. The variousingredients are held together in a hinder, the composition being of sucha viscosity that it is adapted for printing with ordinary printingmachinery. The color changing feature of the composition is provided bythe incorporation therein of a leuco ester of a vat dye which is capableof being printed in its undeveloped vat color. The use of a single dyeingredient in a sterilization indicator coating such as this is highlydesirable because both the undeveloped and developed color of thecoating composition are easily controlled. Furthermore, it does notpossess the undesirable feature of changing color with age which isfound in some of the multi-dye indicating systerns.

It has been found that by incorporating into the composition certainoxidizing and acid splitting agents, the vat color of the dye willdevelop simultaneously as the article or material, on which the dye iscoated, is sterilized. When the coated article has been completelysterilized, the color of the dye has completely developed. The dye inthe composition is retained in its undeveloped state previous tosterilization with the aid of an alkali and an amine, which are held inthe coating by a binder. It is preferred to use ammonium hydroxide and amonovalent tertiary amine. During steam sterilization of the articlesonto which this coating composition is applied, the acid splitting agentliberates an acid, and along with the oxidizng agent, provides an acidoxidizing medium which causes regeneration of the vat dye by oxidizingthe dye in the presence of an acid medium. The acid splitting agent issufficiently strong to lower the pH of the coating from a pH well aboveneutral down to 5 or below.

With the use of certain leuco esters of indigoid type vat dyes, it ispossible to start with a coating composition which is colorless, or onewhich has a pale yellow color, and develop a strong, distinct color.With the use of certain leuco esters of anthraquinonoid type dyes, amuddy brown, maroon, or red color will develop into a bright lue, greenor orange color. In some cases, both the undeveloped and developedcolors are important. For instance, it has been found to be desirable tohave a coating which appears red before sterilization, and greenafterwards, obviously in conformity with the stop and go signals.

While the ammonium hydroxide was incorporated into the compositionspecifically for preventing premature color change, the resultingcoating was found to be acceptable only in certain climates, becauseheat and high humidity conditions would cause premature color changeeven though the ammonium hydroxide held the pH of the composition aboveseven. The mono-valent tertiary amine was incorporated into thecomposition for the purpose of improving printability characteristics.The addition of the mono-valent tertiary amine had the surprising eifectof preventing premature color change of the coating even in warm andhumid climates.

A variety of dyes, acid splitting agents, and oxidizing agents may beused in the coating composition according to this invention. It ispreferred to use an anthraquinonoid type vat dye. Genenally this type ofdye provides a distinct color change as well as having very desirablecolors.

Some of the acid splitting agents found to be effective in the coatingcomposition are as follows: tetraethenol, ammonium hydroxide, ammoniumsulphate, ammonium oxalate, ammonium thiocyanate, ammonium gluconate,and ammonium metavanadate. The oxidizing agent may be, for example,sodium chlorate. The binder is preferably a resinous type binder such aspolyvinyl alcohol, and must be of a viscosity such as to result in acoating composition of printable viscosity. It should also be watersoluble before printing, but water resistant after printing to preventundue fading or funning of the coating when subjected to steamsterilization conditions.

The mono-valent, tertiary amine is characterized as an invert soaphaving colloidal properties. Furthermore, being cationic in nature, itforms a complex which imparts water resistance to polyvinyl alcohol.Without addition of the amine, the polyvinyl al-cohol would not becomeinsoluble in water before sterilization. The polyvinyl alcohol must bewater soluble at the time the coating composition is made up, but it ishighly desirable that it be water insoluble before sterilization toprevent bleeding of the dye.

Ordinarily the amine, being cationic in nature, is incompatible with thedye. Therefore, they must be held together in a colloidal suspension.The protective colloid is a partially hydrolyzed grade of polyvinylalcohol which is an efiective emulsifying agent, and also may have aviscosity low enough for use in inks.

In the examples which follow, Algosol Olive Green IB (CF), AlgosolGolden Yellow IRK, and Algosol Blue IBC are le-uco esters ofanthraquinonoid type vat dyes manufactured by General Aniline and FilmCorporation, and identified in the 1954 Technical Manual and Year Bookof the American Association of Textile Chemists and Colorists. Gelvatol40-10 is a partically hydrolyzed polyvinyl alcohol manufactured byShawinigan Resins Corporation, and Amine O is a mono-valent tertiaryamine manufactured by Geigy Chemical Company. The anti-foam agent usedwas DC Antifoam A emulsion, a produ-ct of Dow-Corning Corporation. Thepercentages used are weight measures.

Also in the examples which follow, the catalyst comprised the following:

57.00 water 8.70% of a 28% solution of ammonium hydroxide 17.15%ammonium gluconate 17.15 sodium chlorate This catalyst contained theacid splitting and oxidizing agents, as well as the alkali for holdingthe pH of the composition up.

The polyvinyl alcohol was added to the cold water. This was heated to150 F. while stirring, during which time the antifoam agent was added.When the polyvinyl alcohol had completely dissolved, the dye was added.After the dye had completely dissolved, the solution was cooled. Thecatalyst was added next, and while mixing, the alcohol was added as asolvent to aid in rendering the composition printable. This coatingcomposition was then printed on paper articles, the coating having aninitial color of maroon. When the articles were exposed to steamsterilization conditions until the articles had been completelysterilized, the coating turned a dark green color. The coating, however,was not sufiiciently resistant to water, and had a tendency to runduring steam sterilization. When the samples of paper coated with thiscomposition were stored for an appreciable length of time underrelatively high heat and relative humidity conditions, the coatingdisplayed a tendency to change dromits initial maroon color to a eencolor even 4. through it had not been subjected to sterilizationconditions.

The polyvinyl alcohol was added to cold water. This mixture was heatedto 15 0 F. while stirring, during which time the antifoam agent wasadded. When the polyvinyl alcohol was completely dissolved, the dyeswere added. After the dyes had completely dissolved, the solution wascooled. The catalyst was added next, and while mixing, the alcohol wasadded as a solvent to aid in rendering the composition printable. Thecoating composition was then printed on paper articles. When thearticles were exposed to steam sterilization conditions until thearticles had been completely sterilized, there was no noticeable changein color of the coating because the developed color of the dyes wasfound to be the same as the undeveloped color. The samples were notsubjected to storage tests to determine the effect of prolonged heat andhigh relative humidity, because of this compositions inability to changecolors when the dyes were developed. Obviously, this composition wouldnot be acceptable.

Example 3 Ingredients of composition:

Percent Polyvinyl alcohol binder, Gelvatol 40-10 20.00 Water 39.20Antifoam agent, D.C. antifoam A emulsion 0.30 Dye, Algosol Olive GreenIB (CF) 10.00 Catalyst 20.00 Anhydrous ethyl alcohol 10.00 Amine, AmineO 0.50

The polyvinyl alcohol was added to the cold water. The mixture washeated to F. while stirring, during which time the anti-foam agent wasadded. When the polyvinyl alcohol was completely dissolved, the dye wasadded. After the dye had completely dissolved, the solution was cooled.The catalyst was added next, and while mixing, the alcohol was added asa solvent to aid in rendering the composition printable. The amine wasadded next. The coating was printed on a paper sample and subjected tosteam sterilization conditions for a time sufficient to effectsterilization. The initial color of the coating was maroon, but thecolor after being subjected to sterilization was green. Like sampleswere also tested in storage under abnormally high heat and relativehumidity conditions. The samples showed no tendency to change colorprematurely under these adverse conditions. Printability on paper wasvery good.

I claim:

1. A composition for printing telltale insignia indicating, by a changein col-or, that sterilization conditions have been attained whichcomprises, by weight, approximately 20% partially hydrolyzed polyvinylalcohol, approximately 40% water, approximately 10% of a leuco ester ofan anthraquinonoid type vat dye, approximately 15% of a catalystcomprising an acid splitting agent, an oxidizing agent, and an alkali,approximately 15 anhydrous ethyl alcohol, an antifoam agent, and amono-valent tertiary amine.

2. A composition according to claim 1 in which said catalyst compriseswater, ammonium hydroxide, ammonium gluconate, and sodium chlorate.

3. A composition for printing telltale insignia indicating, by a changein color, that sterilization conditions have been attained whichcomprises, by weight, approximately 20% partially hydrolyzed polyvinylalcohol, approximately 40% water, approximately 10% of a leuco ester ofan indig-oid type vat dye, approximately 15% of a catalyst comprising anacid splitting agent, an oxidizing agent, and an alkali, approximately15% anhydrous ethyl alcohol, an antifoam agent and a mono-valenttertiary amine.

4. A composition according to claim 3 in which the catalyst compriseswater, ammonium hydroxide, ammonium gluconate, and sodium chlorate.

5. A composition for printing telltale insignia indicating, by a changein color, that sterilization conditions have been attained whichcomprises, by weight approximately 20.00% partially hydrolyzed polyvinylalcohol, approximately 50.60% water, approximately 0.30% antifoam agent,approximately 10.00% of a leuco ester of an anthraquinonoid type vatdye, approximately 10.00% anhydrous ethyl alcohol, approximately 0.50%of a mono- 2 valent tertiary amine, approximately 1.74% of a 28%solution of ammonium hydroxide, approximately 3.43% of ammoniumgluconate, and approximately 3.43% of sodium chlorate.

6. The method of preparing matter for changing color ter.

References Cited by the Examiner UNITED STATES PATENTS 2,606,654 8/1952Davis et al. 252408 2,798,855 7/1957 Hainsworth 252408 3,076,707 2/ 1963Lawton et al 252408 MURRAY TILLMAN, Primary Examiner.

SAMUEL H. BLECH, Examiner.

W. J. BRIGGS, SR., Assistant Examiner.

2. A COMPOSITION FOR PRINTING TELLTALE INSIGNIA INDICATING, BY A CHANGEIN COLOR, THAT STERILIZATION CONDITIONS HAVE BEEN ATAINED WHICHCOMPRISES, BY WEIGHT, APPROXIMATELY 20% PARTIALLY HYDROLYZED POLYVINYLALCOHOL, APPROXIMATELY 40% WATER, APPROXIMATELY 10% OF A LEUCO ESTER OFAN ANTHRAQUINONOID TYPE VAT DYE, APPROXIMATELY 15% OF A CATALYSTCOMPRISING AN ACID SPLITTING AGENT, AN OXIDIZING AGENT, AND AN ALKALI,APPROXIMATELY 15% ANHYDROUS ETHYL ALCOHOL, AN ANTIFOAM AGENT, AND AMONO-VALENT TERTIARY AMINE.